Trend and variability of surface air temperature in northeastern Spain (1920–2006): Linkage to atmospheric circulation

An assessment of long-term change and variability of temperature over northeastern Spain (1920–2006) is provided using a dataset of 19 observatories. In addition, a more detailed analysis of the spatial and temporal variability of maximum, minimum, and mean temperatures, and the diurnal temperature range (DTR) has also been carried out employing 128 observatories spanning the period from 1960 to 2006. In general, maximum, minimum, and mean temperatures have increased significantly, mainly from 1960. Contrarily, the DTR showed less coherent variability with both positive and negative trends. On a seasonal scale, the analysis reveals that the weakest trends (mostly insignificant at the 5% level) were observed during autumn, while the strongest warming rates were found during summer and spring. Spatially, the observed warming was more robust in the coastal proportions compared with mainland observatories. The trends on the annual timescale are spatially consistent with those observed in warm seasons (summer and spring) rather than in cold seasons (winter and autumn). This study also explores the forcing mechanisms that can explain temperature variability on seasonal timescales. This variability can markedly be connected to variations in the large-scale atmospheric patterns. Notably, the Eastern Atlantic (EA), the Scandinavian (SCA), and the Western Mediterranean Oscillation (WeMO) patterns exert a significant influence on temperature variations in the study domain. Our results confirm that circulation patterns have spatially variable influences on temperature on both seasonal and annual timescales. Changes in patterns of atmospheric flows, as driven by increase in zonal circulation and anticyclonic conditions in recent decades, seem to play a noticeable role to explain spatio-temporal variability of temperatures in the study domain.